First up, is that we stop assuming a communicative impairment denotes a cognitive one. Let’s be wary of assuming that behind autism’s speechlessness lies nothing, or nothing to speak of. Instead, let’s assume that we’re dealing with a mind as keen as our own, and act accordingly. Talk to the person. Don’t worry if there’s no evidence he or she understands. Maybe there is evidence, but you’re not recognising it as such. If the person is there, never discuss them as if they’re not, or as if they’re only there like the coat stand is there. If they don’t notice this courtesy, no harm is done; but if they do, then someone who is often treated as a part-object, part-human, total nuisance gets to feel like a real, valid, card-carrying member of society.